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The Constellation Sagittarius - The Archer

Sagittarius is a summer constellation. For Northern Hemisphere observers, it can be seen floating above the southern horizon during the summer months from June through August and into early September. However, by September, it is beginning to set by sunset.

Sagittarius is commonly called "the teapot" because the shape of the stars seems to look like a teapot to modern observers. However, the ancient Greeks and Romans, who named the constellation, thought it looked like a centaur shooting a bow and arrow into the heart of Scorpius, the scorpion. Sagittarius mean Archer.

And easy way to find Sagittarius would be to find the Milky Way overhead in summer. Follow it to the southern horizon, and you should find Sagittarius.

As with all constellations, Sagittarius is best seen in a dark sky outside the city. However, because its stars are relatively bright, you should be able to make out the basic shape even when the moon is up.

Sagittarius is the happy hunting ground of the summer observer. Within it lies the very heart of the Milky Way itself, providing vistas which are unparalleled in grandeur and diversity. Observers at a southerly latitude are provided with views unattainable by their more northerly brethren, for whom this constellation lies just along the southern horizon. Southern Hemisphere observers have the best view, since Sagittarius flies straight overhead when viewed from Australia, South America, and southern Africa..

Diffuse nebulae abound in this region, along with their associated open star clusters. As globular clusters orbit around the center of our galaxy, many of this beautiful class of objects are also found within its boundaries. 

The August 1993 issue of ASTRONOMY magazine highlighted planetary nebulae in this region, and I highly recommend consulting that article. Here, I will only be able to highlight objects which I found to be particularly fascinating, and will almost assuredly leave out somebody's favorite object. The truth is, this constellation is worthy of several night's observing, and not just for Messier objects. Many beautiful non-Messier objects can be found by examining a star chart and pointing a telescope.

SAGITTARIUS

M8 and M20 dominate the summer Milky Way, standing out boldly against the dust and star clouds of the Galactic Center in Sagittarius. Part of M24 can be seen poking in on the upper left, and open cluster M23 is at the top center. Saturn, a non-stellar interloper, shines brightly to the left of M20 in this 200-mm photo made on Konica 3200 film at the Prude Ranch during the 1988 Texas Star Party.

M-8 - The Lagoon Nebula. One of the finest cluster/nebula combinations in the sky. The large, scattered open cluster lies at the eastern edge of a large, swirling cloud of nebulosity. The nebula has obvious dark lanes and looping patterns, which in long exposure photography are shown to dense star forming regions. This is a fine sight in almost any telescope, and is easily seen by both the naked eye and in binoculars.

M-20 - The Trifid Nebula. This often photographed nebula is rather faint in small telescopes, but in moderate size instruments shows a circular patch of light surrounding a double star. Tis patch of light is more or less equally divided by three intersecting dark lanes meeting near its center. A fainter region of reflection nebulosity can be seen to the north.

M-17 - The Omega or Swan Nebula. This is one of my favorite objects in this region. This bright nebula looks like a check mark or swan floating in a heavenly pond. It consists of a curving arc of nebulosity connected to a straighter bar shape. The bar portion shows a lot of intricate mottling and streaks. Photography shows this region to be only a small part of a larger, billowing nebulous region.

M-22 - This is one of the finest globular clusters in the sky visible from northern latitudes. It is large, about 15-20' in diameter, and is rather loosely gathered, allowing us to resolve many individual stars across its face. Some consider this globular to be second only to Omega Centauri in beauty.

M-24 - The Small Sagittarius Star Cloud. This is a large, disconnected portion of the Milky Way. The best view comes in binoculars, which show countless stars and some obvious dark streaks along its length. NGC 6603, which some authors claim erroneously to be M-24, lies in its northeastern section. This is a small, tight open cluster bearing no resemblance to Messier's original description.

NGC 6522 and NGC 6528 - Anyone who has observed with me will not be surprised by my inclusion of these two faint globular clusters in this article. Every time I observe in the summer, my telescope is at some time pointed at these objects. They are small and moderately faint, but lie within the same field of view of a low power eyepiece in a highly populated region of the Milky Way. The longer they are observed, the more background stars become visible, producing a grainy backdrop for these two twin globulars. A great deep sky double!

NGC 6520 and B86 - Another of my personal showpiece objects in Sagittarius, NGC 6520 is a small, rather tight gathering of about twenty stars placed right next to a similarly sized dark nebula, B86. The proximity of the cluster seems to accentuate the darkness of the nebula and make it appear as a hole in the sky, definitely darker than the surrounding region. This dark nebula is commonly known as the Ink Spot because of this.

Article © Copyright Rick Raasch
Photos © Copyright Edward P. Flaspoehler, Jr.

Messier Objects in Sagittarius

Another view of the Lagoon and Trifid Nebulae, photographed on August 14, 1999, using Celestron 80-mm f/5 spotting scope. Five minute exposure on Fuji Color 800 film. Photo copyright by Ed Flaspoehler.

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